Apparatus for releasing threaded pipe couplings



y 5, 1956 w. cs. SWEETMAN 2,745,345

APPARATUS FOR RELEASING THREADED PIPE COUPLINGS Filed Sept. 18, 1948 2Sheets-Sheet 1 WILLlAM G. SWEETMAN IN V EN T 0R.

ATTORNEY y 1956 w. cs. SWEETMAN 2,745,345

APPARATUS FOR RELEASING THREADED PIPE COUPLINGS Filed Sepi. 18, 1948 2Sheets-Sheet 2 WILLIAM G. SWEETMAN INVENTOR.

ATTORNEY FIG. 2-A

United States Patent APPARATUS FGR RELEASING THREADED PIPE C GUPLiNGSWilliam G. Sweetman, Houston, Tex. Application September 18, 194%,Serial No. 49,990 4 Claims. (Cl. 102-2l.3)

This invention relates to an apparatus including a device for releasingthe threaded connection between sections of a pipe string which havebecome stuck in a well in order to permit unscrewing of a portion of thepipe string so that it may be retrieved from the well.

In the rotary drilling of wells, drilling strings are conventionallyemployed which are made up of sections of pipe connected together byheavy screw couplings, commonly called tool joints. Such tool jointsconventionally comprise an internally threaded box member and anexternally threaded pin member adapted to be screwed tightly into thebox member when the joints are made up. Such drilling strings frequentlybecome stuck tightly in a well, whereupon it becomes highly desirable toretrieve a maximum amount of the pipe above the point at which thestring is stuck. Unscrewing of the string from the top of the well isgenerally unsatisfactory because there is no way of assuring that thelowermost joint above the point at which the pipe is stuck will be theone which will unscrew to thereby permit maximum recovery. Also becauseof the tightness with which the joints are normally made up, or becomeset up during use, the unscrewing torque required will often lead totwisting-off of the string, which will result in excessive losses anddamage to the pipe.

Various methods have heretofore been employed to sever the pipe stringat the desired point. These methods include the use of mechanicalcutting tools, explosive and the like. Mechanical cutting is expensiveand time consuming, While shooting with explosives has heretofore beengenerally ineffective and undesirable particularly because of theconsequent damage to the pipe and to the surrounding well bore. Othermethods have attempted to use limited quantities of explosives to jarthe coupling while an unscrewing torque is applied to the pipe stringbut have proven generally ineftective because of the difiiculty ofefiectively localizing the force of the explosive which may result intightening rather than loosening the joint, and may cause excessivedamage to the 1 e. One of the objects of this invention is to provide adevice for releasing a pipe joint whereby such operation may beperformed in a simple and eifective manner and with simpleinstrumentalities.

Another object of this invention is the provision of a novel apparatusfor employing explosives to effect release of pipe sections in a well.

An important object is to provide an apparatus employing explosiveswhich eliectively concentrates the force of the explosive preferentiallyon the female member of a tool joint to effect uniform radial expansionof the same relative to the male member to thereby effectively loosenthe threaded connection therebetween.

Another important object is the provision of a novel apparatus foreffecting the release of a pipe coupling.

Other and more specific objects and advantages of this invention willbecome apparent from the following detailed description when read inconjunction with the accompanying drawings which illustrate one usefulembodiment in accordance with this invention.

In the drawings:

Fig. 1 illustrates a pipe releasing device in accordance with thisinvention in position in a well pipe for effecting release thereof;

Figs. 2 and 2a, together is an enlarged longitudinal sectional view ofthe device shown in Fig. l;

Fig. 3 is an enlarged fragmentary view in longitudinal section of theexplosive member of the device;

Fig. 4 is a cross-section along line 44 of Fig. 3;

Fig. 5 illustrates the suspension of the device from a conventionalweight indicator;

Fig. 6 is a view similar to Fig. 1 showing another embodiment of thisinvention;

Fig. 7 is a view showing the application of the invention to a casing ortubing; and

Fig. 8 is a general view, somewhat diagrammatic in form, showing anotherembodiment of this invention.

Generally stated and in accordance with an illustrative embodiment ofthis invention, the apparatus provides means for producing adjacent thejoint and impinging against one of the joint sections but in a directionaway from the other joint section, an annular gaseous jet of suflicientintensity to loosen the joint, and this jet is axially confined. Whilereleasing of the joint may be accomplished by directing the jetgenerally in the zone of the joint, better results are obtained bydirecting the jet against one of the joint sections. The jet may bedirected inside against the female of the joint to expand it; howeverthe jet may be also directed against the outside of a male section tocompress it. In each case, the purpose is to release the joint so it canbe disconnected.

The device for releasing the joint can be exceedingly simple; thus itmay comprise a carrier shaped to extend circumferentially of the jointwhen placed adjacent thereto, and this carrier may be provided with adetonatable chemical charge shaped anuularly to direct an annularaxially confined jet against the joint, and preferably against one ofthe joint sections as heretofore noted. The carrier may be shaped to beplaced interiorly of and adjacent the joint, particularly where theexpansion is to be of the female section; the carrier may however beshaped to pass over the pipe joint where the male section is to becontracted. Suitablemeans may be provided for locating the carrieradjacent a joint in order to act thereon.

Referring to the drawings, Fig. 1 shows the device in position in aconventional tool joint, indicated generally by the numeral 19,preparatory to elfecfing release thereof. Tool joint 10 consists of atubular box 11 and a tubular pin 12. Box 11 and pin 12 are connected toadjacent sections of a pipe string 13. Box 11 has a tapered internallythreaded portion 14 and is provided with an internal shoulder 15 spacedsomewhat below the lower end of threaded portion 14. Pin 12 has acorrespondingly tapered threaded portion 16 insertible into box 11 andengageable with the threads therein. Pin 12 is provided with anoutwardly extending shoulder 17 at the upper end of threaded portion 16which is adapted to engage the upper end of box 11 when the joint ismade up. The length of portion 16 of the pin is conventionally madesomewhat less than the depth of threaded portion 14 of the box so thatwhen the joint members are fully made up, the inner end of pin 12 willbespaced above shoulder 15 providing an annular recess 18 in the jointbetween shoulder 15 and the inner end of pin 12. As noted, such tooljoints are entirely conventional and are normally of standardizeddimensions throughout, the

wall thickness of the pin and box members being generally much thickerthan the walls of the pipe sections which are connected togetherthereby.

The releasing device in accordance with this invention is showngenerally in Fig. 1 and in detail in the other figures. The deviceconsists generally of a firing head 20 having a shock absorber 21, amember 22, which will be referred to as a joint locator which istelescopically. connected to shock absorber 21, a weighting member orsinker bar" 23 connected to joint locator member 22, and a cableconnection 24- connected to the upper end of sinker bar 23 and having,in turn, connected thereto a lowering cable 25 through which is threadedan elec- 'trical current conducting cable 26. j

Referring now to Figs. 2, 2a and 3; firing'head 20 comprises acylindrical body 23 having an upwardly. extending boss 29 provided inits exterior surface with a plurality of longitudinal grooves3 ll 'Box29 and body 28 are provided with an axial boreBl which is reduced indiameter in its lower end asat 32. Body 23, is adapted to be insertedinto the upper end of a tubular. sleeve 33 which is closed at its'lowerend'by an end wall. 34'having upwardly and outwardly taperinginner'corners 35 A threaded connection, indicated at 36, is providedbetween the upper end of sleeve 33 and the exterior of body 28 toprovide a tight connection there'oetween and a compressible packingring, such as a. conventional O ring 37, is suitably arranged belowthreaded connection 36 between the adjacent surfaces of body 23 andsleeve to provide a iluid-tight seal therebetweenr With the describedarrangement, end wall 34 will bespaced from the lower end of body 28 toprovide a chamber adapted to contain a charge of suitable detonatingexplosive, indicated generally by the numeral 38. The lower end ofsleeve 33 is provided. with a downwardly extending boss 39 provided atits lower end with a laterally extending flange 49, A plurality ofspring fingers 41 are mounted in circurneferentially spaced relation inflange 40 and extend upwardly and radially outwardly therefrom intocompressive engagement with theinner wall of joint 16. The upper ends 42of fingers 41 are preferably first bent slightly outwardly and theiruppermost tips are then bent inwardly slightly sothat as the fingers arecompressed inwardly in passing downwardly over the inner walls of pipe13 and joint 10, ends 4-1 will pass over any protuberances or pits whichmay be present along these walls but when drawn upwardly will snap intoany substantial recesses, such as recess 18, and engage the upper wallthereof, such as is formed by the lower end of portion 16 of V the tooljoint pin. The lower ends of fingers 41 extend through suitableperforations in flange 40 and are bent inwardly at 43 to seat in radialgrooves 44 provided in the lower face of flange 49. A washer 45 isclamped against the bent ends 43 of the fingers by means of a stud 46which. is screwed into the lower end of boss 39, to thereby firmlyfasten the fingers to flange 40.

Charge 38 comprises a body of a suitable detonating chemical 47 which ismolded or pressed into a generally disk shape having an axial orifice 48therethrough. The outer peripheral face of the charge is hollowed at 49.

The hollow may be V-shaped or arcuate and is lined with acorrespondingly shaped liner 50 which may be constructed of thin copper,steel, or other. suitable metal. For convenience chemical 47 may be.formed of symmetrical half disks having suitably shaped peripheries, so

that when two of them are placed side-by-side, in the arrangementillustrated, they will together form the charge 47 having the requiredperipheral hollow shape.

The outer diameters of the charge and liner 50 are dimensioned so thattheir outer edgeswill be flush with the inner wall of sleeve 33 and willfit snugly there-against when the firing head is assembled. Whennecessary or desirable additional half-disks of the explosive may beplaced, as illustrated, on opposite sides of the main charge tosupplement the mass and, therefore, the power of the charge. Corners 35serve as fillers for the tapered outer edge of the lower half-disk,while a suitably shaped filler ring 51, constructed of metal orrigid'pla'stic material, will be arranged, as illustrated, about theedge of the upper half-disk of the explosive.

Orifice 48 is filled with a charge of a suitable booster explosive 52,preferably in the form of a pile of short cylindrical pellets. A 'fuzeelement, indicated generally by the numeral. 53, comprises a cylindricalelectrical '1 the bushing which is, in turn, in electrical contact withthe other metallic parts of the device.

Boss 29 carrying the fuze element extends into the lower end of the boreof a sleeve 21a and is connected thereto by means of setscrews 53 whichextend radially through the wall of sleeve 21a into grooves 30. Withthis arrangement sleeve 21a is connected to firing head 20 so as toprevent relative rotation therebetween while permitting a limited degreeof relative longitudinal movement as determined by the lengthof grooves30.. A resilient bumper ring 59, constructed of rubber or like resilientmaterial, is placed about boss 29 between the upper edge of body 28 andthe lower end of sleeve 21a. Extending from the upper end of the bore ofsleeve 21a is an elongated axially bored stem 6%, having an enlargedhead 61 at its upper end. The lower end of stem is held in place in thebore of sleeve 21a by means of radial set-screws 62 extending throughthe wall of sleeve 21a into engagement with the end of the stem.

Stem 60 is slidably inserted in the bore of a tubular cylinder 63, thelower end of which is closed by a tubular bushing 64 surrounding stem60. A coil spring'65 is mounted in cylinder 63 surroundingstem 60 and isheld in compression between head 6land bushing 64. Stem 6%, cylinder 63and coil spring 65 together generally comprise'the joint locator element22, previously referred to; An elongated slot 66 is cut through the wallof cylinder 63 and forms a guide for a stud 67 extending laterally fromthe upper end of stem 60 between the side wall of slot 65;

whereby relative longitudinal movement between stem 60' 63. Sleeve 21aand bumper rings 59 and 68 constitute the shock absorber element 21. Theupper end of cylinder 63 is provided with a screw socket 69 in the baseof which is seated an electrical contact 70 from which a conductor wire71 leads downwardly through the bore of stem 60 into the bore of sleeve21a where it is connected to the upper end of electrode 56. Socket 69 isadapted to receive a tubular threaded pin 72 carried by the lower end ofsinker bar 23, which is axially bored' to receive a conductor wire 73which is connected at its lower end to an electrical contact 74 mountedin the bore of pin 72 and adapted to make electrical connection withcontact 70' when pin 72 is screwed tightly, into socket 69. Itwill beunderstood that the upper end of conductor wire 73' is connected to asimilar electrical contact (not shown) i 1 which will be engaged by anelectrical contact carried by cable connection 24 and connected toconductor cable 26 when cable connection 24 is connected to the upperend of the sinker bar in the conventional manner. cable 25 with itsenclosed conductor cable 26 extend to the surface and pass over a pully74 (Fig. 5) which is resiliently supported by a conventional weightindicator,indicated schematically at 75, which is, in turn, suspended bya line 76 from the usual derrick (not shown). Weight indicator 75 may beof any of the conventional electrical'or mechanical forms adapted toregister or record, as on the dial 77, small changes inthe weight of thestring of tools supported by pully 74. Itwill be understood that cable25 passes to a reeling drum (not shown) of conventional design employedto raise and lower the well. end of cable 25, while conductor cable 26is connected to a suitable source of electric current for supplyingfiring current to the device.

Lowering Explosive 47 and booster 52 may be made of one or more of manywell known chemical substances of the type generally designated asdetonating explosives which, upon detonation, decompose very rapidly togenerally gaseous decomposition products which are capable of attainingextremely high velocities, particularly when suitably controlled anddirected in accordance with the method and apparatus of this invention.Numerous chemicals of this character are available for use in accordancewith this invention including such materials as pentaerythritoltetranitrate (PETN), Tetryl, Pentolite (50% PETN and 50% TNT),trinitrotoluene (TNT), Amatol, Cyclonite, Tetrytol (60% Tetryl and 40%TNT), and many others well known to those familiar with such detonatingchemicals. The explosive chemicals will ordinarily be used, aspreviously noted, in the compressed and molded form.

The above described device is operated in the following manner: Thedevice, assembled as illustrated in the drawings, will be suspended fromlowering cable 25 and lowered thereby through pipe 13. Ordinarily, thelowermost point at which the pipe is free will have been previouslydetermined by means which are well known in the industry and the depththereof from the top of the well measured. The releasing device will belowered to approximately the indicated point, spring fingers 41 beingcompressed as the tool passes downwardly through the pipe and connectingtool joints. When the device has reached its lowermost point of travel,the cable will be carefully drawn upwardly at the top of the well untilthe upper ends of fingers 41 come in contact with the recesses 18 in thefirst of the tool joints above the point of maximum descent. Ends 42 ofthe fingers will expand into the recess and engage the lower end of pin12 in that joint, thereby efiectively lodging the device in the joint atthat point and resisting further upwardly movement of the cable. Thelength and point of attachment of fingers 41 to firing head will bedimensioned with respect to the relative elevation of charge 38, so thatwhen the upper ends of the fingers have engaged the end of the tooljoint pin, the hollowed face of the charge will be opposite the wall ofbox 11 a short distance below the end of pin 12. This is very importantbecause it is essential that the major portion of the force of thecharge should be preferentially concentrated on the wall of box 11. Whenthe device has thus lodged in the tool joint, the upward strain on thecable will compress coil spring 65 by drawing cylinder 63 upwardlyrelative to stem 60 above bumper ring 68, as indicated by the solidlines in Figs. 1 and 2a. This compression of coil spring 65 will betransmitted through weight indicator 75 to dial 77, appearing as anincrease in weight thereon, and will thereby immediately apprise theoperator at the surface that fingers 41 have engaged the tool joint. Thecontraction of the coil spring acts to take the tensile load ofi offingers 41 due to the upward pull on the cable, while at the same timeproviding the warniug indication to the operator that the fingers havelodged, otherwise, and particularly when operating at depths of severalthousand feet, the drag of the heavy cable and attached tools wouldcompletely mask the pull resulting from the lodgment of the relativelyweak fingers in the joint recess and the fingers might be pulled out ofthe recess without the operator becoming aware of this occurrence. Theweight indicator recording or registering device will normally be socalibrated with respect to the strength of coil spring 65, that eachinch of contraction of the latter will indicate a predetermined weightincrease on the weight indicator. Also coil spring 65 will be selectedof a suitable strength with respect to that of fingers 41, so that thecoil spring will contract two or three inches or more, for example,before fingers 41 will collapse under the tension applied to the cable.Thus, as soon as the operator observes a change in wieght indicationcorresponding to a contraction of say two inches in coil spring 65, hewill know that fingers 41 have lodged in the selected joint and willimmediately stop further upward pull 6' on the cable. During descent ofthe tool the frictional drag of fingers 41 on the pipe wall will allowcylinder 63 to move downwardly into contact with bumper ring 68, as

H indicated by the broken lines in Figs. 1 and 2a, and the weight ofsinker bar 23 and cylinder 63 will thus be imposed on the lower membersof the device, thereby overcoming the resistance of the fingers andacting to push the device downwardly, as previously noted.

With the device now in position, firing current will be transmittedthrough conductor cable 26 to set oil the charge. When the charge isdetonated the gases generated thereby will be caused to converge byreason of the shape of hollow 49 and liner 50 into an annular radiallydirected jet or blast which will cut through the wall of sleeve 33 andstrike a corresponding annular area on the inner wall of box 11. Theforce of the concentrated explosive blast will be uniformly distributedin a narrow annular band about the inner wall of box 12 and willuniformly expand it radially outwardly and eifectively loosen theengagement of the box threads from the threads on pin 12. The explosionwill ordinarily destroy most of the firing head 20 but bumper rings 59and 68 will act to absorb the recoil of the device and efiectivelyprotect sleeve 21a and the upper elements of the device from damage.These parts will all be withdrawn from the well, after which, byapplying suitable unscrewing torque to the pipe string at the top of thewell, the entire string above the joint in which the explosion is setoil can be unscrewed and withdrawn from the well. It will be found thatlower pin 12 will be entirely undamaged and can be re-used. Tests madeon subsequently recovered boxes in which the releasing device has beenemployed, show that these too are virtually undamaged except for aslight increase in their internal diameters.

By suitably varying the angles of hollow 49 and liner 5%, the degree ofconcentration of the explosive force, and, therefore, of the pressureexerted against the box, may be varied as desired. An angle of about 90will be found to be generally satisfactory for most cases but may bevaried from about to 100 the angle in each case being generallysymmetrical about a central horizontal plane through the charge. With anangle of the major part of the explosive force will be concentrated in ahorizontal plane. As the angle is enlarged, the explosive force willdiverge correspondingly and strike a somewhat wider annular area of thebox with a consequent reduction in the pressure per unit of area.Reduction in the size of the angle will correspondingly converge theexplosive force on a narrower annular area with consequent increase inpressure per unit of area. It will be understood, however, that thequantity of explosive and the size of the angle of the hollow will beadjusted in each case to produce a force below that which would resultin cutting or bulging the metal of the box. By employing supplementalhalf-disks arranged on opposite sides of the main charge, in the mannerillustrated in the drawings, that is, with their peripheries taperingtoward the horizontal axis of the main charge, the explosive force oftheir detonation will serve to further confine and concentrate the forceof the main charge generally along its horizontal axis. Suchsupplemental charges will ordinarily be used when relatively heavypressures are desired.

Body 10 will ordinarily be made of steel or aluminum while sleeve 33will ordinarily be constructed of aluminum or other relatively easilyshatterable metal but may be made of any suitable rigid plastic materialadapted to withstand the hydrostatic pressures when the device is usedinside a pipe which is filled with fluid.

Fig. 6 illustrates a modification applicable to joints in which thepositions of box 11 and pin 12 are reversed relative to the arrangementshown in Fig. 1. To provide for properly locating firing head 20 inrelation to the box an adapter 78 carrying fingers 41 is screwed to thelower end of boss 39 and is made of suitable length relative to thedimensions of the joint so that when the endsof. the; fingers. lodgeinre'cess, 18 or against shoulder 15,. charge 38 will be opposite thewall of box 11 and properly spaced axially relative to the end of pin12. Themethod of operation including location of the selected joint willbe the same as previously described;

Fig. 7 illustrates a modification of this invention as applied to casingor tubing in which the sections of pipe are joined by a double-endedfemale screw coupling. In this embodiment sections of pipe 79 are shownconnected together by a conventional female screw coupling 80. In suchconnections the ends of the pipe sections normally do not meet even whenfully made up, so thatthere will usually be provided an annular recess,as at 31, in which fingers 41 may engage, as in the previously describedembodiments. In this. modification the length of fingers 41 will beadjusted so that when they are engaged in recess 81', thehorizontal axisof the hollow in charge 33 will be aligned with the portion of coupling80 which is exposed thereto through recess 81. When the charge, sopositioned, is fired, the axially confined annular jet will strike theexposed inner face of coupling 80 through recess 81 and expand thecoupling to thereby loosen the joint.

Fig. 8 illustrates another embodiment by which a joint may be loosenedby compressing the male member from the exterior thereof. Thisembodiment is shown applied to a tubing or casing joint such as thatillustrated in Fig. 7. In this embodiment an annular carrier 82 isemployed which is adapted to slide downwardly over pipe 79 and coupling80. Carrier 82 has mounted therein a ringshaped explosive charge 83 theinner periphery of which is hollowed and provided with a correspondinglyhollowed liner 34, as illustrated. A lowering cable 85 is employed tolower the carrier down the outsideof the pipe and an electricalconductor cable 86 is connected to a fuze 87, of generally conventionalform, which is inserted into detonating relation to charge 83. Carrier82 is provided with a plurality of depending spring fingers 88, thelower ends of which are bent upwardly and inwardly generally as shown.With this arrangement, the carrier may be loweredalong the pipe, fingers88 serving to center the carrier about the pipe so that it will passfreely over any couplings above that which is to be loosened. When theproper point is reached and an upward pull taken on cable 85, the endsof fingers 88 will lodge against the lower edge of the coupling nextabove the point of maximum descent. This will space the charge justabove the upper edge of the coupling, as illustrated, so that the jettherefrom will strike the adjacent'portion of the male end of the pipesection and compress or contract it suificiently to loosen it in thejoint.

It will be understood that various changes and alterations may be madein the details of the apparatus embodiments herein described within thescope of the appended claims but without departing from the spirit ofthis invention. While this invention is particularly designed for therelease of a joint between sections of a pipe string in a well, it isuseful for other applications.

' What I claim and desire to secure by Letters. Patent is:

1. Apparatus for releasing the threaded joint between the members of amale-female threaded coupling connecting pipe sections in a well,comprising, a carrier insertible in the bore of said couplingand movablelongitudinally therein on a lowering cable, a continuous annular highexplosive charge mounted on said carrier concentric with said coupling,said charge being composed of a pair of superposed fiat rings ofdetonatable explosive having registering axial bores and complementaryinwardly sloping peripheral edges to define between them a continuousannular hollow in the outer periphery of said charge, said hollow beingtriangular in cross-sec tion and having an included angle of from about80 to 100, a body of booster explosive disposed in said axial bores, aliner conforming in shape to and seated insaid hollow, acircumferentially extending wall closing said hollow at its base,radially extending resilient spacer elements mounted on said carrier andengageable with the inner end of the male member of said coupling inresponse to upward movement by said cable to thereby selectivelyposition said charge within the female memberof said coupling andaxially spaced from said inner end of said male member, a resilientconnection means interposed between said carrier and said cableextendible by upward pull on said cable following engagement of saidspacer means with said inner end of said male member, and detonatingmeans on said carrier positioned on the longitudinal axis of saidcharge.

2. An apparatus according to claim 1 wherein said resilient connectionmeans comprises a pair of telescopically connected tubular members, anda coil spring arranged in compression between said tubular members.

3. An apparatus for releasing the threaded joint betveen the members ofa male-female threaded coupling connecting pipe sections in a well,comprising, a-cylindrical body insertible in the bore of the coupling, aclosed cylindrical: chamber in said body, a continuous annular, highexplosive charge enclosed within said chamber, said charge comprisingapair of superposed fiat rings of detontable explosive havingregistering axial bores and having complementary inwardly slopingperipheral edges to define between them a peripheral hollow oftriangular cross-section having an included angle of from about to abody of booster explosive disposed in said axial bores, the base of thetriangular hollow being substantially flush with the inner face of thewall of said chamber, a thin metallic liner conforming in shape to andseated within said hollow, means for positioning said body in thecoupling with said hollow directed toward the female member thereof andaxially spaced from the male member thereof, and detonating means onsaid body positioned in detonating relation to said charge on itslongitudinal axis.

4. Apparatus for releasing the threaded joint between the members of amale-female threaded coupling connecting pipev sections in a well,comprising, a carrier in-' sertible in the bore of said'coupling, acontinuous annular high explosive charge mounted on said carrierconcentric with said coupling, means on said carrier for selectivelypositioning said charge within the female mem: ber of said coupling andaxially spaced from thernale member of the coupling, said charge beingcomposed of a pair of superposed fiat rings of detonatable explosivehaving registering axial bores and complementary inwardly slopingperipheral edges to define between them a continuous annular hollow inthe outer periphery of said charge-:1 body of booster explosive disposedin said axial bores, a liner conforming'in shape to and seated'in saidhollow, said hollow and liner being triangular in cross-- section withan included angle of from about 80 to 100, 2. circumferentiallyextendingwall closing said hollow at its base, and detonating means mounted insaid carrier and positioned to detonate said charge on its longitudinalaxis.

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